Looking around, the astronaut would see a landscape of small hills, of crumbling dust and occasionally huge depressions that are the entrances to a vast subterranean network of constantly shifting caverns.

On a comet, geysers of gas and dust erupt into space, many starting their journey below the horizon. When they reach up into the sky, they are twisted into curious spirals by the nucleus's spin.

Some geysers start in shadow and then dramatically burst into sunlight as the jets are caught by the solar wind and are blown away from the Sun.

At this stage of the comet's orbit, no stars would be visible to a surface astronaut - the sky would be too full of glowing gas.

Stars would only be visible when the comet receded into the cold outer Solar System where it would freeze and become a small inert world.

Hanging motionless

Gravity is slight, so an astronaut could jump into space and take weeks to come back down again. They could watch the nucleus rotate beneath them.

As well as gravity, other forces come into play because of the comet nucleus's small size and rapid spin. The astronaut could stride to the cometary equator where so-called Coriolis forces are apparent.

Throwing snowballs of cometary material into the air, the astronaut would see these missiles curve in seemingly illogical directions. They could even be tossed against the comet's spin and appear to hang motionless in space.

No manned cometary landings are planned and probably never will be because of the dangers involved. However, the unmanned Rosetta spacecraft will release a small probe to touch down on Comet 67P/Churyumov-Gerasimenko in 2014.